The present invention relates generally to systems and methods for producing metal alloys, and more particularly to a method for selecting alloying elements for complex, multi-component amorphous metal alloys in the production of amorphous phase metal alloys in bulk form.
Amorphous metallic alloys have unique mechanical and physical properties attributed to the atomic structure of the amorphous phase. Generally, high cooling rates above 105 K/s are required to produce amorphous alloys in ribbon, flake or powder form, with the resulting sample thickness less than 50 xcexcm (Luborsky (Ed), Amorphous Metallic Alloys, Butterworths, London (1983)), and efforts have been made to consolidate the material into bulk form. New multi-component alloy systems with lower critical cooling rates ( less than 102 K/s) have been developed that can produce fully amorphous products by conventional casting to thickness up to about 100 mm (Inoue, Progress in Materials Science, 43 (1998) 365-520); Johnson, in Johnson et al (Eds), Bulk Metallic Glasses, MRS Symposium Proceedings, 554, Materials Research Society, Warrendale, Pa. (1999) 311-339; Inoue, Acta Materialia, 48 (2000) 279-306). Most of these bulk amorphous alloys contain very expensive elements of platinum and/or lanthanum groups that limit their application, and only zirconium-based alloys not containing these elements have found successful use (see Johnson, supra).
After the discovery of amorphous alloys, attempts were made to understand the amorphization mechanism in order to predict alloy compositions with better glass forming ability. Three empirical rules were defined for the bulk amorphous alloy systems (Inoue, Acta Materialia, supra), namely, (a) requires three or more elements: (b) difference in atomic size ratios above about 12% among the three main constituent elements; and (c) negative heats of mixing among the three main constituent elements. The glass formation composition range usually coincides with a eutectic region, and a reduced glass transition temperature, Trg=Tg/Tm, as high as 0.6-0.7 is typical for easy glass formers (Davies, in Luborsky, supra, 8-25). (Tm is the absolute liquidus temperature and Tg is the absolute glass transition temperature.) The density difference between the amorphous and fully crystalline states for bulk amorphous alloys is in the range of about 0.3-0.54%, smaller than the 2% characteristic of ordinary amorphous alloys (Matgumoto (Ed), Materials Science of Amorphous Alloys, Ohmu, Tokyo (1983); Yavari et al, in Johnson et al (Eds), supra, 21-30). This indicates that bulk amorphous alloys have higher dense randomly packed atomic configurations than ordinary amorphous alloys. Formation of the liquid with specific atomic configurations and multi-component interactions on a short-range scale have been suggested to increase the solid/liquid interfacial energy and decrease atomic diffusivity, which, in turn, leads to suppression of nucleation and growth of crystalline phases (Inoue, Acta Materialia, supra). Topological complexity and frustration were given (Johnson, supra) as another explanation of suppression of crystallization in the multicomponent alloys.
The empirical rules are rather general, and new amorphous alloy development has remained a time-consuming, labor-intensive trial and error process of selection,and screening various element combinations using empirical selection guidelines and requiring expensive laboratory equipment to test candidate alloys. Specific criteria for selection of easy glass forming alloy systems would significantly advance the art. The importance of atomic size and critical concentration of alloying elements in phase stability is summarized in empirical Hume-Rothery rules, and a fundamental basis for these rules has recently been identified (Egami et al, J Non-Cryst Solids, 64 (1984) 113-134), leading to development of a topological criterion for metallic glass formation (Egami et al, supra; and Egami, J Non-Cryst Solids, 205-207 (1996) 575-582). According to this criterion, a minimum concentration of alloying elements required for amorphization decreases continuously with increased difference in atomic sizes of solute and solvent elements. This behavior is typical for ordinary amorphous metals with a critical cooling rate greater than 104 K/s, but the behavior is not typical for bulk amorphous alloys, and the criterion is therefore not useful for the specification of bulk metallic glasses.
The invention solves or substantially reduces problems with previously existing metal alloy specification approaches and methods by providing a method for selecting alloying elements for complex, multi-component amorphous metal alloys. In this method, the atom radii of selected elements are plotted along the x-axis and the concentrations in atomic percent (at %) are plotted along the y-axis. Each alloying element forms a single point and all points for a given alloy provide a distribution of atomic sizes and concentrations that characterize the system. The alloying elements are selected so that the solvent is the largest atom with a concentration of 40-80 at %. The next most concentrated element has the smallest radius within 65-83% of the radius of the solvent atom and a concentration in the range 10-40 at %. Other elements are selected at lower concentrations and have atomic radii within 70-92% of the radius of the solvent atom, so that a single, broad, concave upward atomic size distribution plot is obtained. In the preferred embodiment, alloys with four or more elements are specified, where at least one of the other solute elements has an atomic radius within 70-80% and at least one has an atomic radius within 80-92% of the solvent atom radius. The concentration of elements that have radii that differ by less than 1% from one another are added together and treated as a single alloy addition for the purpose of this invention.
It is a principal object of the invention to provide bulk amorphous metal alloys.
It is another object of the invention to provide an improved method for producing amorphous metal alloys.
It is another object of the invention to provide a method for predicting alloying element concentrations in production of bulk amorphous metal alloys.
It is another object of the invention to provide a method for producing amorphous metal alloys in bulk form with a minimum dimension of one mm or more.
It is a further object of the invention to provide a method for producing bulk amorphous metal alloys for use in construction, electronics, medicine, sports, and other applications as would occur to the skilled artisan practicing the invention.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.
In accordance with the foregoing principles and objects of the invention, a method for selecting alloying elements for complex, multi-component amorphous metal alloys is provided in which the solvent element is the largest atom with a concentration of 40-80 at %, the second most concentrated alloying element has a radius of 65-83% the radius of the solvent atom and a concentration of 10-40 at % in the alloy. Other alloying elements are selected at lower concentrations and have atom radii of 70-92% of the radius of the solvent atom. In the preferred embodiment, alloys with four or more elements are specified, where at least one of the other alloying elements must have an atomic radius within 70-80% and at least one must have an atomic radius within 80-92% of the solvent atom radius. The concentrations of elements that have radii that differ by less than 1% from one another are added together and treated as a single alloy addition for the purpose of this invention.